Tools are attached to casing strings, drill strings, or other oilfield tubulars, to accomplish a variety of different tasks in a wellbore. Such tools may include centralizers, stabilizers, packers, cement baskets, hole openers, scrapers, control-line protectors, turbulators, and the like. Each tool may have a different purpose in a downhole environment, and each may have a different construction in order to accomplish that purpose. However, each is generally attached around the outer diameter of the oilfield tubular.
When deployed into the wellbore, the tools may abrade or spall by engagement with a surrounding tubular (e.g., a casing, liner, or the wellbore wall itself). Further, the tools may engage foreign bodies in the well, such as cuttings or other bodies, as are known in the art, which may also wear the tools. Accordingly, wear-resistance and a low coefficient of friction may be valuable characteristics for the downhole tools.
One way to enhance the material properties of the exterior of the tools is to weld another material thereto. This is referred to as “hardbanding.” Hardbanding, however, generally includes the application of intense heat for the welding process, which may damage the underlying tool structure. Thermal spraying is thus sometimes used for the coating process. Thermal spraying may include melting and spraying a material onto the tool (or another substrate) to be coated. Thermal spraying, however, generally results in poor bonding and poor structural characteristics when built up to thick layers. Furthermore, thermal spraying often employs materials that include high levels of chromium, which presents health and safety issues and may require special handling procedures and equipment.
Furthermore, connecting the tools to the tubular may present challenges. The tools may be connected directly to the tubular, or a “stop collar” may be fixed to the tubular, e.g., between the pipe joints, which may be configured to engage the tool. One way to connect the tool or stop collar to the tubular is by welding it to the tubular. As with hardbanding, however, the strong hold of a weld may come at the expense of damaging the tubular and/or the tool, e.g., by creating a heat-affected zone (HAZ) in either or both. The HAZ may represent an area of the tubular where the metallurgical properties are altered, which may translate into diminished strength, corrosion resistance, or certain other characteristics. Accordingly, in some applications, an HAZ may be avoided.
Set screws and/or adhesive are thus sometimes used to attach a tool to a tubular, since these attachment methods do not create an HAZ. However, set screws and adhesives may not provide adequate holding force for the tubular, and/or may not be sufficiently corrosion or heat resistant.